The present invention relates to a torque convertor composed of a pump, a turbine and a stator which form a hydraulic-fluid circulating tubular toroid.
The pump, turbine and stator of the torque convertor constitute three types of wheels having vanes which transmit torque by the agency of a hydraulic fluid.
Torque convertors have been disclosed in which the degree of "flatness" with respect to the cross section of the toroid formed by the three vane wheels is increased. The consequently reduced axial length of the torque convertor provides advantages of weight reduction and increased efficiency of power transmission, and facilitates the multi-stage capacity of the transmission itself. Additionally, the reduced dimension of the toroid in the axial direction of the convertor allows room for the installation of a lock-up device having multiple discs.
However, the modified vane wheels tend to generate eddies in the hydraulic fluid as it is passed through, such that the fluid furthermore collides with the vanes, degrading the performance of the torque convertor. Consequently, it is desirable to retain comparable performance characteristics in a torque convertor having its toroid components modified to increase the axial flatness of the convertor.
A torque convertor disclosed in Japanese Patent Laid-Open No. 57-37791 has flattened toroid components providing torque convertor performance which is up to par. The flatness ratio L/H, wherein L is the length of the tubular toroid in the axial length of the convertor and H the length in the radial direction thereof as well, is set within the range of 0.64 to 0.87. According to these specifications, however, the tubular toroid can't be sufficiently flattened to provide the necessary accommodation room along the axial direction of the torque convertor.